Demand for energy is growing continuously and the actual trend is to shift some energy consumption to electricity. Within the next few years, plug-in electric vehicles will be on the market in growing numbers and without load management, the only alternative for meeting the growing demand is to build more electric power plants and reinforce the power-grid. Renewable and decentralized generations will add more challenges for load management.
Load management aims to balance the supply of electricity on the grid with the electrical load. This can be achieved by real time direct control of some appliances by the utility or by using variable tariffs to influence consumer behaviour. There are many techniques for load management, some of them acting on water heaters. Most of them use direct control where user appliances are controlled by the electric utility and control is applied to groups of users on a given schedule. So only a limited number of water heaters consume electricity at the same time during the peak period. In such techniques and without an appropriate controller, user comfort can be affected if a water heater's temperature drops below the comfort level. There is no feedback from the water heater to the electric utility in order to control each water heater separately and the water heater has no control to do it on its own.
Another known concept is the Smart Grid which is a form of network that delivers electricity from suppliers to consumers using two-way digital communications to control appliances at consumers' homes for saving energy, reduce costs and increase reliability and transparency if the risks inherent in executing massive information technology projects are avoided. The Smart Grid is envisioned to overlay the ordinary electrical grid with an information and net metering system that includes smart meters.
The idea of communications from suppliers to consumers to control appliances is not new, and systems have been implemented using analog technology for many years. The growth of an extensive digital communication network for the internet has made it practical to consider a more sophisticated type of electric Grid. The increased data transmission capacity has made it conceptually possible to apply sensing, measurement and control devices with two-way communications to electricity production, transmission, distribution and consumption parts of the power grid at a more granular level than previously. These devices could communicate information about grid condition to system users, operators and automated devices, making it possible for the average consumer to dynamically respond to changes in grid condition, instead of only utilities and very large customers.
Like existing utility grids, a Smart Grid includes an intelligent monitoring system that keeps track of all electricity flowing in the system, but in more detail. Like the existing grid, it also has the capability of integrating renewable electricity such as solar and wind, but has the potential to do so more effectively. When power is least expensive the user can allow the Smart Grid to turn on selected home appliances such as washing machines or factory processes that can run at arbitrary hours. At peak times it could turn off selected appliances to reduce demand.
Smart Grid deployment is under way in many countries. This transformation enables new capabilities that involve an important change regarding load management. With the Smart Grid, electric utilities are deploying advanced meters and devices with microprocessors and two-way communication that allow it to better control the grid, to interact with the customers and to collect real time information about their electricity usage, etc.
Microsoft presents their vision of Smart Grid, referring to it as “smart energy ecosystem”, by proposing a “Smart Energy Reference Architecture” (SERA). Web services are part of their vision. Whirlpool proposed architecture called Whirlpool Smart Device Network (WSDN) that includes the Internet as part of the communication infrastructure. Cisco delivers an IP-based communications infrastructure for the Smart Grid. Lately, they announced a partnership with Itron who will embed Cisco IP technology within its OpenWay® meters.
However, the transformation to the grid presents a large challenge for the implementation of load management measures, not to mention the challenges added by plug-in electric vehicles and decentralized electric generations.
An overlay network is a virtual network that is adapted to run on top of a physical network. It is used for a wide number of applications such as media streaming, peer-to-peer file sharing, multicast communication, virtual reality, quality of service (QoS), video and voice calls (VoIP), etc. Participant nodes are adapted to create and build the virtual network. Moreover, the participant nodes are adapted to organize themselves in a topology that allows them to exchange information.
The topology is chosen according to the communication protocols and applications that use the overlay network. For instance, resilient overlay networks preferably require topologies that have a higher level of redundancy with respect to the physical network. Video streaming and file sharing applications preferably require topologies that respect the capabilities of the source.
A network topology can be unstructured or structured. In unstructured systems there are redundant connections that improve the quality of service but increase the overhead necessary to maintain a loop free structure. In structured systems it is easier to have a loop free structure and a simple routing algorithm.
Depending on the applications and protocols some topologies may be better adapted than others; a tree topology decreases the communication delay but presents a center point failure and is not optimized for many-to-many communication. A ring topology increases the number of links but the communication delay increases with the number of nodes in the ring.
An overlay network topology can be hierarchical, having ordinary nodes on one level and super nodes on another level. It can be hierarchical and structured such as a cubic or a tore network topology. However, none of these topologies is well adapted for applications where millions of nodes need to send continuously flowing messages to the entire network. This functionality is required for some applications where a large number of intelligent communicating devices such as intelligent sensors or controllers exchange information continuously in order to achieve a common goal.